Audiences will fall for Jason Segel and Emily Blunt in “The Five-Year Engagement” only to have second thoughts long before the end credits roll.

The new romantic comedy from the creative team behind “Forgetting Sarah Marshall” boasts some mid-sized laughs that don’t involve intestinal distress or disgusting hair gel.

We’re even treated to a serio-comic exploration of gender roles in the 21st century – not a bad appetizer to go along with the main comedy course. But the film loses its grip on both the narrative and the appealing characters mid-film, turning a smartly crafted romance into a numbing march to another pat movie resolution.

The trouble begins when Violet is offered a plum university job in Michigan, forcing Tom to quit his lucrative job as a sous chef and push back their wedding date. Violet quickly bonds with her new work mates, including a handsome university adviser (Rhys Ifans) and her fellow postdoc pals (including “The Office’s” Mindy Kaling and “Think Like a Man’s” Kevin Hart).

Tom can only find work making sandwiches at a no-frills eatery, a lazy storytelling trick that assumes mid-westerners don’t enjoy fine dining. He grins and bears it – for a while.

But circumstances continue to prolong their engagement, all the while a chasm grows between them more formidable than Michigan’s freezing winters.

For a good hour, the humor in “Engagement” comes from the characters and the changing mores of modern relationships. Years ago, the men rose up the corporate ladder while the women grinned while smoothing out their starched aprons. Now, men and women are expected to simultaneously chase their dreams, causing the kind of marital friction that can’t be assuaged with any book on tape-born advice.

You can literally feel “Engagement” spin off its axis mid-film. Tom embraces the a hearty Michigan lifestyle, hunting his own food and making an odd drink from honey, all the while sporting a lumberjack’s beard.

It’s an out of character flourish that feels disingenuous, but it’s merely the first of many such moments. It’s hard not to wince at the awkwardly constructed bow and arrow sequence to follow, a calamitously staged bid for laughs that shuts the movie down cold.

Later, more plot devices are introduced, each less convincing than the last. Characters take on new hues to fit the story, making us regret caring for Tom and Violet in the first place.

Blunt and Segel fit, to put it mildly. He’s overgrown but tender, while she’s gorgeous but magically approachable. And when they fight, it’s often with bruised but believable consequences, like when he asks to be alone, but not for Violet to actually leave their bed, you know?

“The Five-Year Engagement” wins us over early, but we’re ready to see other rom-coms long before Tom and Violet’s love story wraps.